During the link initialization phase of the establishment of high-speed wired network communications, it is necessary for the two ends of the link to communicate in order to establish link rate, exchange link capabilities, and to adjust equalizer settings. This communication is commonly referred to as “backchannel” communication. For simplicity and cost savings, it is desirable that the backchannel be the same channel as is eventually utilized for data mode communications. When backchannel communication is initiated, the link rate may not have been established and link capabilities may not be known. Further, prior to adjusting equalizer settings, bit errors related to link characteristics (e.g., frequency response) may be prevalent. Equalizer adjustment is generally performed at a link operating rate (link rate). At the link rate, bit errors may degrade communication making reliable backchannel communication at the link rate difficult if not impossible prior to and/or during equalizer adjustment.
One solution is to provide a backchannel communications mode at a relatively lower bit rate and an equalizer adjustment mode at a higher bit rate, i.e., at the link rate. This solution requires mode shifting between the backchannel mode and the equalizer adjustment mode. Such mode shifting is undesirable as it adds time to the initialization process and requires synchronization between the two ends of the link. Such mode shifting also requires that the receiver equalizer be retrained (Infiniband method) after a mode shift, or that the receiver equalizer be frozen (Ethernet method) during backchannel communications. As link speeds increase, equalizer retraining or freezing assumes an increased level of risk with respect to repeatability and unexpected adaptation behavior.
Although the following Detailed Description will proceed with reference being made to illustrative embodiments, many alternatives, modifications, and variations thereof will be apparent to those skilled in the art.